Methods are known from prior art in which a container, in particular a bottle, is produced from a blank made of plastic. For this purpose, the blank is at least thermally conditioned and is then shaped hydraulically to form the container in a mould during a shaping phase, as a result of a liquid pressurized material being introduced into the blank while the blank is axially and radially stretched.
In most known methods, a so-called stretch rod is used for axial stretching which is introduced into the blank through the mouth of the blank which later represents the container opening. Using the stretch rod, a mechanical force is exerted on the base of the blank such that the thermally conditioned blank is stretched axially. The greatest force is thereby required for initiating the stretching procedure. It is important to initiate the axial stretching in a controlled manner such that the future container is formed evenly and the wall thickness reaches the desired values.
The use of a stretch rod during the hydraulic shaping with liquid filling material, however, has the disadvantage that the stretch rod must be immersed in the filling material and filling material always remains on the stretch rod on removal from the filled container which can contaminate the filling machine or the container outer sides. In particular in the case of liquids containing sugar or the partial filling of the container with syrup, this leads to contamination which must be avoided.
A method is known from DE 10 2011 015 666 A1 in which a guiding and shaping device engages with the blank from the outside during the stretching. It is thereby difficult to transfer the tensile forces required to initiate the stretching to the blank such that these forces must be applied primarily from the inside by the exertion of pressure of the filling material flowing in. However, the force acting radially and axially can thereby not be differentiated between such that the initiation of the axial stretching is problematic.